The present invention relates to an air-conditioning system, particularly to an air-conditioning system in which an energy recovery apparatus is installed. Furthermore, the present invention also relates to a method of installing the energy recovery apparatus.
In a general form of a regenerative air-conditioning system, as shown in FIG. 9, from a thermal storage tank 6, water is fed to air-conditioning loads (A. H.) 9 such as a heat source machine or a fan coil via a pump 7, and water passed through the air-conditioning load 9 is led into the thermal storage tank 6 via a return pipe line 10. This is referred to as an open return process. The open return process is used in a case where an actual pump head is less than 20 m. When the air-conditioning system comes to a stop, water supply from a feed pump is stopped. However, in the open return process, water freely falls in the vertically rising return pipe line, that is, water drops under the gravity. A siphon effect by the dropping water causes the pressure in the pipe line to be negative so as to induce cavitation noise, vibration, and corrosion result. To eliminate these problems, a vacuum breaker 12a is installed to prevent the pressure in the piping from becoming negative. An energy recovery apparatus for an open return type regenerative air-conditioning system is described in JP-A-63-297949. A structure is shown in FIG. 11.
From the thermal storage tank 6 arranged in a basement of a building, water is fed to a heat source machine 24 on a roof of the building via the pump 7, and is fed to air-conditioning loads 29 on respective floors via another pump 27. The water fed to the air-conditioning loads 29 passes through a return pipe line 22 so as to return to the heat storage tank 6 installed in the basement. Energy recovery apparatuses 100 are installed on a third floor and the first basement in the return pipe line.
On the other hand, in recent years, even with the construction of high-rise buildings, regenerative air-conditioning systems have also been used in buildings with about five to ten floors. In this case, since the actual pump head exceeds 20 m, there is a problem that large vibration and noise are caused upon dropping of water in the open return system. To prevent occurrence of such problems, pressure sustaining valve 11 is disposed in the return pipe line 10 before the water is returned to the heat storage tank 6 in order to prevent the water from dropping. This is a full water return process which is configured in general as shown in FIG. 10.
The pressure sustaining valve 11 is one of pressure regulating valves. When a pressure larger than a set pressure is applied, the valve opens so as to allow water to pass therethrough. On the other hand, when the air-conditioning system comes to a stop and the water supply from the feed pump 7 is interrupted, the valve is rapidly closed in order to prevent water from dropping. From the time when the water supply from the feed pump 7 is interrupted to the time when the pressure sustaining valve 11 closes (three to ten seconds), water in the vertically rising return pipe line 10 freely falls, that is, water is dropped under the gravity in the same manner as in the open return process. In order to prevent the pressure in the pipe line from becoming the negative pressure at this stage, a surge tank 13 is connected via a check valve 12b. Thus water is fed from the surge tank 13 until the pressure sustaining valve 11 is closed, and the pressure in the pipe line is prevented from becoming negative.
When the air-conditioning system comes to a stop the water supply from the feed pump 7, the pressure sustaining valve 11 has to prevent water in the return piping 10 from dropping. Therefore, the set pressure of the pressure sustaining valve 11 stored to be set to a value slightly larger than a pressure which is exerted to the valve when the valve is closed. The pressure exerted to the pressure sustaining valve 11 when the feed pump 7 resting is equal to a potential energy owned by water in the return piping 10, or a height to the water surface of the surge tank 13 from the pressure sustaining valve 11, that is, the actual pump head. In other words, the pressure sustaining valve 11 has a resistance corresponding to the actual pump head. That is, during the operation of the air-conditioning system, water is fed via the feed pump 7, the potential energy of water pumped up to a top part of the pipe line in the air-conditioning system by the feed pump 7 is consumed as the resistance of the pressure sustaining valve 11 when water passes through the pressure sustaining valve 11. Therefore, since no energy remains in return water downstream of the pressure sustaining valve 11, the energy recovery apparatus cannot be used.
On the other hand, should the energy recovery apparatus be connected, upstream of the pressure sustaining valve 11, the potential energy of the return water would not be absorbed by the energy recovery apparatus just upstream of the pressure sustaining valve 11, the water cannot flow overcoming the resistance of the pressure sustaining valve 11, and therefore the air-conditioning system cannot be operated normally.
Moreover, the power of the feed pump 7 has to be increased in order to operate the air-conditioning system in the state in which the energy recovery apparatus is connected, upstream of the water drop preventing valve 11, and accordingly, there would be raised a problem that energy saving cannot be achieved.
Furthermore, if the energy recovery apparatus is connected upstream of the pressure sustaining valve 11, the pressure of the pressure sustaining valve could be set to be small, that is, the resistance of the water preventive valve 11 could be set to be small, and accordingly the consumption power of the feed pump 7 can be restrained from increasing. However, the actual pump head owned by the return water could not be maintained by the pressure sustaining valve 11 when the air-conditioning system comes to a stop, and there would be raised such a problem that water drops. It is to be noted that the pressure sustaining valve is installed in the air-conditioning system, in the basement or the like and it is difficult to remove the valve.
Additionally, if the energy recovery apparatus fails, a problem similar to such a problem that an obstruction is caused in the return pipe line occurs, and therefore the air-conditioning system cannot be operated normally.